Field of the Invention
The present invention relates to an optical method for the determination of anionic groups in a stream, and optionally for the determination of the turbidity of the stream. If desired, the stream can be fractionated, according to the particle size or mass of any substances therein, or both size and mass, prior to the determination(s).
Description of Related Art
Charged groups originating from pulp suspensions and other slurries can have a significant effect on the behavior of the slurry in chemical reactions. These charged groups can react with and bind to various additives and particles added to the slurry, as well as cause flocculation. Therefore, determining the content of such charged groups is important in determining the amount of additives to be used, and to determine whether these charged groups need to be separately removed.
Some of the methods traditionally used for measuring the content of anionic groups in a sample have been labor- and time-consuming. Simpler alternatives include titration (conductometric or potentiometric) of laboratory samples of the slurry. However, these methods cannot be performed directly in flowing stream, and they require that the anionic groups are in their protonated form.
An alternative optical method is described in WO2004063724 and F1991963. In W02004063724 the sample is first washed in order to remove dissolved and small particles from the pulp fibers. Dye is added, the sample is filtrated and the amount of unadsorbed dye is measured. In F1991963, the change in absorbance is measured as a function of added anionic or cationic polymer from which a calibration curve is constructed. This method requires time consuming titration of a separate laboratory sample, and it requires a calibration curve to be constructed for each different type of sample. Thus, these methods both require additional steps such as washing and filtration of the sample, and the measurements in both methods are carried out on laboratory samples, and do not allow direct measurement in a flowing stream.
These methods are based on the measurement of one single wavelength, rendering them sensitive towards interference. Therefore they do not provide a reliable result of the charge. These methods also require a calibration.
Therefore, there exists a need for methods of determining the total charge of streams or their particle populations, which methods should be fast, simple and possible to carry out directly on flowing streams, whereby separate sample collection can be avoided.